MINIREVIEW: Cytokines: An Expanding Network of Immuno-lnflammatory Hormones

The term lymphokine was introduced nearly 20 yr ago (1) to denote nonantibody, protein mediators of cellular immunity produced by activated lymphocytes. Monocyte products were subsequently termed monokines, but with the realization that other cells involved in immuno-inflammatory responses, e.g. endothelial cells, neutrophils, marrow stromal cells, and fibroblasts were also sources of lymphokines and monokines, these mediators have come to be known generically as cytokines. Originally, cytokines were designated according to their bioassays and their names abbreviated to appropriate acronyms, e.g. lymphocyte activating factor (LAF) (Table 1). Almost as many cytokine activities have been identified in crude supernatants from heterogeneous cell populations stimulated by various means as there are individual bioassays. With their purification and cloning, it has become apparent that most of the proteins responsible for these activities have multiple, overlapping actions (2, 3); hence, their multiple acronyms, e.g. LAF and endogenous pyrogen are the same monocyte product now called interleukin 1 (IL-1). The international interleukin nomenclature adopted for cloned cytokines has been applied most recently to IL- 6, previously known either as B cell stimulatory factor- 2, B cell differentiating factor, hybridoma-plasma and growth factor, hepatocyte stimulatory factor, or interferon β2 (4, 5), and to IL-7 (6) (Table 1). However, some cloned cytokines, e.g. the interferons (IFNs) (7, 8) and hemopoietic colony-stimulating factors (CSFs) (9, 10) retain their original names for historical reasons.